Nannostomus rubrocaudatus – Purple Pencilfish

In live fish colour pattern is perhaps the most useful way to identify N. rubrocaudatus plus the closely-related N. marginatus and N. mortenthaleri. N. marginatus is immediately distinguished from the other two by the fact it lacks red pigmentation on the body in males, but N. mortenthaleri and N. rubrocaudatus are more easily-confused. Males of N. rubrocaudatus can be told apart fro...